Differences in Kidney Function Estimates Based on Creatinine and/or Cystatin C in Non-Traumatic Amputation Patients and Their Impact on Drug Prescribing

• Main Authors: Mia Aakjær, Morten B. Houlind, Charlotte Treldal, Mikkel Z. Ankarfeldt, Pia S. Jensen, Ove Andersen, Esben Iversen, Lona L. Christrup, Janne Petersen
• Format: Article
• Language: English
• Published: MDPI AG 2019-01-01
• Series: Journal of Clinical Medicine
• Subjects: Creatinine; cystatin C; glomerular filtration rate; renal insufficiency; amputation; drug therapy; drug dose adjustment; drug dosing; inappropriate prescribing
• Online Access: http://www.mdpi.com/2077-0383/8/1/89

Accurate kidney function estimates are necessary when prescribing renally-eliminated medications. Our objectives were to investigate how amputation affects estimated glomerular filtration rate (eGFR) and to determine if dosing recommendations differ among different eGFR equations. In a cohort study of non-traumatic amputation patients, eGFR based on creatinine and/or cystatin C were measured before and after amputation. Prescribed, renally-eliminated medications were compared with dosing guidelines in Renbase®. Data from 38 patients with a median age of 75 years were analyzed. The median (range) eGFR was 65 (15–103), 38 (13–79), and 48 (13–86) mL/min/1.73 m2 before amputation and 80 (22–107), 51 (13–95), and 62 (16–100) mL/min/1.73 m2 after amputation for eGFRCreatinine, eGFRCystatinC, and eGFRCombined, respectively (p < 0.01). From before to after amputation, eGFR increased on average by 8.5, 6.1, and 7.4 mL/min/1.73 m2 for eGFRCreatinine, eGFRCystatinC, and eGFRCombined (all p < 0.01), respectively. At least one renally-eliminated medication was prescribed at a higher dose than recommended in 37.8% of patients using eGFRCystatinC, 17.6% using eGFRCombined and 10.8% using eGFRCreatinine. In conclusion, amputation affects eGFR regardless of the eGFR equations. The differences among equations would impact prescribing of renally-eliminated medications, particularly when switching from creatinine to cystatin C.